Thursday, October 28, 2010

Newfound Octopus Impersonates Fish, Snakes

 Sea snakes. Changing its color to imitate the yellow and black bands of the toxic sea snake, the octopus threads six of its arms into a hole and waves the other two arms in opposite directions so they look like two snakes.

The researchers think the octopus also may be able to impersonate other sea creatures such as sand anemones, stingrays, mantis shrimp, and jellyfish. For now, however, the scientists will only say for sure that the octopus can mimic sole, lion fish, and sea snakes.

"Mimicry has an element of subjectivity to it," said Tregenza. "You have to be fairly careful. No other octopus has really been shown to mimic another animal."

Long Overlooked

One reason why the researchers had not discovered the octopus previously is that it lives in a habitat that's not very appealing to scuba diversa muddy and relatively barren landscape that lacks the variety and splendor of life found in coral reefs.

"We also think that is why it has such a dramatic [mimicking ability]," said Tregenza. "It has nowhere to hide. It could burrow, or try and mimic one of the animals also found in their environment."

"These boring environments are just the place where you might see the most exciting behavior of animals," he added.

The researchers believe the recently discovered octopus uses its mimicry to avoid predation by large fish rather than as a mechanism to trick its prey. They also think it probably evolved from another species of octopus that's active during the day in coral reefs nearby.

"It may have moved to open ground to harness the many crustaceans and fish found in these habitats," said Norman. "Individuals which looked like dangerous animals were clearly selected for, while others were quickly nailed by passing barracuda, sharks, or groupers. Hence, mimicry was selected for."

The fact that the octopus can adopt so many different animal impersonations greatly reduces its likelihood of encountering predators. This is advantageous, said Tregenza, because if a predator fish often saw a lion fish that looked suspiciously like an octopus, the predator would eventually be more willing to risk being poisoned by taking a bite of its preythus blowing the octopus's cover.

Tregenza said the octopus may decide which creature to impersonate depending on what particular predator is near. Evidence of such behavior came from observations showing that when the octopus was attacked by territorial damselfishes, it mimicked one of the fishes' common predators, the banded sea snake.

"If the mimic octopus can figuratively use its mimicrythat is, can choose to use a particular form in response to a particular threatthis could potentially dramatically improve the defensive value of its mimicry behavior," said Tregenza.